Cloud computing has been increasingly widely applied. More enterprises and individuals are willing to upload their data to a cloud server for storage, so as to save storage costs.
A security issue of data sharing or data backup of a cloud service is a big challenge. If, out of security consideration, cloud consumers (including enterprises and users) encrypt their data before uploading the data to a cloud server, the cloud server cannot read encrypted data of users, and in this way, security and privacy of user data are ensured. For example, before uploading a large quantity of multimedia files (including audios, videos, pictures, and the like) to a cloud server for backup, a user first encrypts the multimedia files locally (for example, on a user terminal).
However, when local multimedia files of the user are lost, and the user wants to retrieve some multimedia files backed up in the cloud server, because pictures backed up in the cloud server are encrypted, the user needs to locally download the large quantity of multimedia files stored in the cloud server and locally decrypt the encrypted backup multimedia files, and then view decrypted multimedia files one by one and determine which multimedia files are needed. In the method for searching for an encrypted multimedia file from a cloud server, a specific multimedia file cannot be quickly found in a large quantity of multimedia files.